This invention relates generally to balancing of rotors, and more particularly concerns method and apparatus for quickly and efficiently reducing a rotor blade out-of-track condition, and for determining the amount of weight to be added to or subtracted from predetermined positions on the rotor, after out-of-track is remedied.
It is a well known fact that a slight out of balance condition of an aircraft rotor, such as a propeller can cause roughness and vibration leading to premature wear and failure of the machine, and fatigue and annoyance of pilot and passengers. In the past, techniques used to correct out-of-balance in the field were crude, time consuming and inaccurate. For example, the mechanic would randomly add a weight to one of the several possible points of weight addition. The pilot and mechanic would fly the ship and try to judge whether the ship felt rougher or smoother; or the same. If rougher, the weight addition would be shifted to an opposite point; if then smoother, more weight would be tried (although it might really required less). If the same, another point would be tried. Generally, this would not lead to a smooth rotor, so weights would be added at another angular position, and the whole operation repeated. By repeating this procedure many times, vibration might be lessened, but the achievement of desired reduction was extremely unusual, because while the pilot could sense vibrational amplitude arising from rotor imbalance, he could not readily sense phase characteristics, and thus had no way of determining the locations for adding weights.